Building REST APIs with ASP.NET Core

Introduction to ASP.NET Core

ASP.NET Core is a cross-platform, high-performance framework for building modern APIs and web applications.

Creating a Web API Project

# Create new API project
dotnet new webapi -n MyApi

# Add NuGet packages
dotnet add package Microsoft.EntityFrameworkCore.SqlServer
dotnet add package Microsoft.EntityFrameworkCore.InMemory

# Run the application
dotnet run

Controller Example

using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;

namespace MyApi.Controllers;

[ApiController]
[Route("api/[controller]")]
public class UsersController : ControllerBase
{
    private readonly ApplicationDbContext _context;

    public UsersController(ApplicationDbContext context)
    {
        _context = context;
    }

    // GET: api/users
    [HttpGet]
    public async Task<ActionResult<IEnumerable<User>>> GetUsers()
    {
        return await _context.Users.ToListAsync();
    }

    // GET: api/users/5
    [HttpGet("{id}")]
    public async Task<ActionResult<User>> GetUser(int id)
    {
        var user = await _context.Users.FindAsync(id);

        if (user == null)
        {
            return NotFound();
        }

        return user;
    }

    // POST: api/users
    [HttpPost]
    public async Task<ActionResult<User>> CreateUser(User user)
    {
        _context.Users.Add(user);
        await _context.SaveChangesAsync();

        return CreatedAtAction(nameof(GetUser), new { id = user.Id }, user);
    }

    // PUT: api/users/5
    [HttpPut("{id}")]
    public async Task<IActionResult> UpdateUser(int id, User user)
    {
        if (id != user.Id)
        {
            return BadRequest();
        }

        _context.Entry(user).State = EntityState.Modified;

        try
        {
            await _context.SaveChangesAsync();
        }
        catch (DbUpdateConcurrencyException)
        {
            if (!UserExists(id))
            {
                return NotFound();
            }
            throw;
        }

        return NoContent();
    }

    // DELETE: api/users/5
    [HttpDelete("{id}")]
    public async Task<IActionResult> DeleteUser(int id)
    {
        var user = await _context.Users.FindAsync(id);
        if (user == null)
        {
            return NotFound();
        }

        _context.Users.Remove(user);
        await _context.SaveChangesAsync();

        return NoContent();
    }

    private bool UserExists(int id)
    {
        return _context.Users.Any(e => e.Id == id);
    }
}

Entity Framework Configuration

// Models/User.cs
public class User
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
}

// Data/ApplicationDbContext.cs
public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }

    public DbSet<User> Users { get; set; }
}

// Program.cs
var builder = WebApplication.CreateBuilder(args);

builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseInMemoryDatabase("MyDatabase"));

builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();
app.UseAuthorization();
app.MapControllers();

app.Run();

Best Practices

• Use async/await for database operations
• Implement proper error handling
• Use DTOs for request/response
• Enable CORS properly
• Use dependency injection